Although many methods of applying these organic metal compounds to the glass to form the metal oxide layer are known, spraying, after the dissolution thereof in a solvent, preferably an organic solvent, is the most widely used method. Indeed, spraying makes it possible to obtain very fine and well calibrated particle sizes and, therefore, a thin and particularly uniform metal oxide deposit.
The solutions are sprayed onto the glass sheets which are still warm from the production line or which have been previously heated to approximately 550.degree. to 640.degree. C. Evaporation of the solvents is, thus, induced as well as a pyrolysis of the metal compounds which, as they decompose, give rise to a layer consisting of at least one metal oxide on the glass. It is possible to deposit in this way the oxides of almost all the plurivalents non noble metals, particularly the metals of Groups IIIB, to VIII and III A to V A of the Periodic Table, advantageously, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Si, Zr, Cd, In, Sn, Sb, Bi, Ce, and, more specifically, the oxides of chromium, iron, cobalt, nickel.
Depending on the oxides to be deposited, the most varied mineral or organometallic compounds, tin chloride, tin dibutyllaurate, titanium or zirconium alcoholates, acetyl acetonates of chromium, iron, cobalt, indium, and the like, have been used to the extent that they possess the requisite stability and ease of use, each with its own specific properties, i.e., its own advantages or disadvantages in terms of uniformity, adhesion of the deposits, ease of use, output, and operating costs, and the like.
All types of solvents have been used according to the particular metal compound, either individually, or in a mixture, including aromatics such as benzene, toluene, aliphatics such as heptanes, white spirit, chlorinated solvents (trichloroethylene and dichloromethane), or oxygenated solvents such as ethanol, methanol, isopropanol, ketones and also esters such as ethyl or butyl acetates.
A known method of producing tin oxide conducting layers is that of combining chlorinated and fluorinated compounds with organic tin compounds such as tin dibutyl oxide in the solution used to treat the surface of the glass.
However, the best results to date in the production of conventional semi-reflecting windows seem to have been obtained by the use of beta-diketonates and acetylacetonates.
Benzene, in particular, is often used as a solvent for acetylacetonates which, among the beta-diketonates, comprise the most often used class of complex salts. Benzene dissolves acetylacetonates particularly well, but has serious drawbacks from the standpoint of health hazards owing to its toxicity. The same is true for dichloromethane, which is highly volatile, or trichloroethylene.
Attempts have also been made to replace benzene by other solvents which have fewer drawbacks, but, since acetylacetonates are less soluble in these solvents than in benzene, the quality of the semi-reflecting glass products obtained after spraying and pyrolysis is much lower.
In pursuing the object which consists in trying to replace benzene by a less dangerous solvent, it has also been suggested to use organometallic salts comprising long hydrocarbon chains dissolved in aliphatic solvents as these salts, particularly the higher beta-diketonates, dissolve particularly well in the solvent.
It has, unfortunately, been noted that the increased solubility obtained, for example, in going from a 5 to 10 carbon atom chain, is accompanied by a decrease in the pyrolytic yield owing to the increasing length of the hydrocarbon chain of the organometallic salt.
As an example, the inventor has used C.sub.8 beta-diketonates of metals such as titanium (III), vanadium, chromium, iron, cobalt, aluminum, silicon, zirconium, indium, in a heptane solution and copper, zinc, titanium (IV), and indium in ethyl acetate, to effect deposits on glass sheets at approximately 600.degree. C. It was, however, noted that the pyrolytic yield was lower which, taking into account the higher cost of C.sub.8 beta-diketonates with respect to acetylacetonates, leads to a higher overall utilization cost. In addition, there was noted, for certain deposits, a less satisfactory adherence to glass.
It was also possible to envisage the use of a mixture: for example, isovaleroylacetonate in large proportions of up to 10 times the initial concentration can be added to a saturated solution of an acetylacetonate in a solvent.
By way of example, chromium isovaleroylacetonate (CrIVA) up to a concentration of 3% of Cr or a total concentration of 3.3% by weight of Cr can be added to a saturated solution (up to 0.3% by weight of Cr) of chromium acetylacetonate (CrAA) in methanol. However, this type of solution has proved of little use as it not only possibly complicates the choice of operating conditions, but, in any event, the two bodies are deposited virtually independently of one another.
In summary, the known state of the art, therefore, leads to the following alternatives for the production of semi-reflecting windows by the spraying of organometallic salts in solution and pyrolysis of these salts:
either in using acetylacetonates dissolved in aromatic or chlorinated solvents which gives a quality product, produced at low cost, but with all the drawbacks associated with the use of these solvents, PA1 or in using organometallic salts with longer hydrocarbon chains which makes it possible to eliminate these drawbacks, but leads to a more costly product and which, in certain cases, shows less adherence although with a greater homogeneity of the deposit.